(CNN) -- Long before the sun even hinted at lighting the sky Sunday, an American soldier left the remote combat outpost of Camp Belambay, allegedly headed for two villages in the Panjwai district of Afghanistan's Kandahar Province.
The district is notorious as a hotbed of Taliban activity, even considered the cradle of the militant movement, though one resident swore she hadn't seen Taliban fighters in months.
She was one of many villagers who had fled the area but returned recently. The Americans on the nearby military base, she said, assured them the area was safe; that no one would bother them.
In the early hours of Sunday, most villagers were in their homes, asleep. They were used to the sounds of helicopters whirring overhead and night raids conducted by U.S. troops.
An Afghan soldier at Belambay spotted a soldier going out around 3 a.m., past the blast barriers, and notified U.S. commanders.
The commanders immediately ordered a head count, as the military always does. They confirmed a soldier was missing and assembled a search party right away, according to Gen. John Allen, the U.S. and NATO commander in Afghanistan.
"It was as that search party was forming that we began to have indications of the outcome of his departure," Allen said.
In the villages, witnesses said, an American soldier began going house to house, seeking out Afghan men, women and even children. Inside the mud walls, they were caught off guard by the intruder.
Then came the unimaginable.
The American pointed his gun at them and fired.
He pulled a boy from his sleep and shot him in the doorway, according to one witness. Then he came back inside the room and put a gun in the mouth of one child and stomped on another.
Streams of dark crimson smeared the drab surroundings and dampened the parched earth. Shell casings littered the ground.
When he was finished, 16 people, including nine children, were dead -- 11 belonged to one family. Several others were wounded.
The soldier dragged some of the bodies out and set them afire.
With carnage behind him, the soldier left.
The search party formed to find the missing soldier came across the suspect, who turned himself in, the military said. He is at the Kandahar detention facility, about 15 miles away, as the United States decides whether to send him back home.
The suspect, a staff sergeant in his 30s, is based at Joint Base Lewis-McChord near Tacoma, Washington. He belongs to the 3rd Stryker Brigade Combat Team, 2nd Infantry Division, according to a congressional source not authorized to speak publicly.
He was trained as a sniper and learned to kill from 800 meters away. The Army has not yet identified him.
He was on his first tour of Afghanistan but had deployed to Iraq three times. In 2010, he'd suffered a traumatic brain injury in a vehicle accident. But few details have surfaced about motive or why an infantryman would turn his gun on civilians.
The Afghans in the mostly farming communities were in a state of utter shock. One man's actions had turned their simple villages into a grisly scene.
The next day, investigators arrived to pick through the horror. A dead toddler with a bloodied face lay in the back of a pickup truck between the bodies of two men. In another were people with charred legs and feet.
Villagers could not conceal their tears.
But their grief soon turned to the kind of anger already festering against Americans after Quran burnings at Bagram Air Base and a video of Marines urinating on bodies.
Though U.S. commanders insisted this was the work of a rogue soldier, some residents believed it to be more calculated. They said more than one soldier was involved.
The Taliban called for retribution in the form of killings and beheadings, adding to the fears of already nervous foreigners in Afghanistan.
Muhammad Wali said his fellow villagers have lost confidence in the Americans as well as Afghan security forces. Both had failed to protect them, he said.
No one knows what will happen next, Wali said. The nature of the war, more than 10 years running, had shifted now that an American had killed ordinary Afghans in the sanctuary of their own homes.
CNN's Sara Sidner, Barbara Starr, Deirdre Walsh, and journalist Ruhullah Khapalwak contributed to this report.